Method for the manufacture of an oxidation stable bright stock



United States Patent 3,011,972 METHOD FOR THE MANUFACTURE OF AN OXIDATiON STABLE BRIGHT STGCK William B. Watson, Park Forest, and Maurice K. Rausch,

Harvey, 111., assignors to Sinclair Refining Company,

New York, N.Y., a corporation of Maine No Drawing. Filed Feb. 25, 1957, Ser. No. 641,857

1 Claim. (Cl. 208264) Our invention relates to the manufacture of bright stocks which are of enhanced stability to oxidation.

Normal processing methods employed in the production of high quality bright stock lubricating oils and in particular those derived from mixed base Mid-Continent crude consist of the following sequence: vacuum distillation of a light reduced crude to yield a heavy lube residuum as bottoms, propane extraction of the lube residuum to remove undesirable asphaltic components and yield a deasphalted oil, solvent extraction of the deasphalted oil with solvents such as phenol or furfural to remove sludge forming aromatic compounds and yield a waxy rafiinate, solvent dewaxing of the waxy rafiinate with solvents such as a mixture of methyl ethyl ketone and toluene to remove the waxy petrolatum fraction and yield a low pour point oil, and an earth adsorptive process to effect color improvement utilizing either clay contact or percolation techniques to yield the finished bright stock oil.

Bright stock oils produced by the above refining sequence usually fall in the 85 to 100 viscosity index range and have utility in such applications as engine oil and industrial lubricant base stocks.

However, for certain severe applications where appreciably longer oil life is demanded, these normal bright stock oils are somewhat lacking in oxidation stability properties. While increased oxidation stability may be attained by higher severity propane deasphalting and solvent extraction treating, this route becomes quite expensive due to the high loss in yield to low quality lay-products.

In accordance with our invention, we have devised a method whereby bright stocks having substantially improved oxidation stability properties can be made from mixed base Mid-Continent crudes. We accomplish this by subjecting to a hydrogenation treatment a bright stock which has been manufactured in a particular manner.

Thus, the bright stock which is hydrogenated is one made by the steam or vacuum distillation of a Mid-Continent crude, preferably a light reduced crude, to obtain an asphalt-containing bottoms which has a SSU viscosity at 210 F. of from 300 to 1200 seconds, the exact viscosity being dependent upon the viscosity desired in the finished lube. The bottoms are then deasphalted to yield a deasphalted oil (extract) which has a Conradson carbon residue not exceeding 225 percent. Suitable deasphalting procedures are well known in the art, and among the deasphalting agents which can be utilized are light hydrocarbons such as ethane, propane or butane, or the Duo-Sol process which employs two solvents which are propane and a mixture of phenol and cresol.

After the deasphalting the lube oil fraction is then solvent extracted under conditions that will yield an oil which after dewaxing has a viscosity index of at least 85. A wide variety of solvents can be employed for the purpose of extracting the deasphalted oil, and among the ones which are best known are furfural, phenol, dichloroethyl ether (Chlorex), nitrobenzene and aniline. After the solvent extraction has been performed, the solvent treated oil is then dewaxed to yield a bright stock which has a viscosity index of at least 85 and an ASTM pour point not higher than 20 F. The dewaxing can be carried out using conventional procedures, so that among the solvents which are useful in the dewaxing step are mixtures of a ketone, such as acetone or methylethyl ketone, and benzene or toluene or a mixture of benzene and toluene; propane; ethylene dichloride, trichloroethylene; normal butyl ketone; and mixtures of benzene and sulfur dioxide.

in hydrogenating the bright stock thus prepared, a cobalt molybdate supported on alumina catalyst is utilized when our invention is practiced. Various methods for manufacturing such catalysts have been described in the art, such as in Byrns Patent 2,325,033, and the catalysts generally consist essentially of from about 2 to 5 percent by Weight of cobalt oxide and from 5 to 15 percent by weight of molybdic oxide, the balance being alumina. Suitable catalysts can also be prepared as described in Teter et al. application Serial No. 514,693, filed June 10, 1955. In the hydrogenation operation, a temperature of from 500 to 725 F, a pressure of from 300 to 700 p.s.i.g. and a weight hourly space velocity (weight units of oil per weight unit of catalyst per hour) of from 3 to 15 are used. The bright stock is hydrogenated while it is in admixture with from 500 to 2000 standard cubic feet of hydrogen per barrel of the charge oil, and the operation is carried out in such manner that the hydrogen consumption amounts to from 10 to 30 standard cubic feet of hydrogen per barrel of bright stock feed.

This sequence of distillation, deasphalting solvent extraction, dewaxing and hydrogenation yields bright stocks which have substantially improved oxidation stability properties.

A specific example which illustrates our process is as follows:

EXAMPLE A mixed base Mid-Continent light reduced crude obtained by atmospheric distillation of a whole Mid-Continent crude to 50% bottoms was vacuum distilled to remove lube distillate streams as overhead and side stream fractions and yield a heavy lube residuum as bottoms. This material tested 15.2 API gravity and 820 SUS at 210 F.

This heavy lube residuum was then solvent deasphalted using propane as the solvent to extract desirable oil components and leave the undesirable heavy asphaltic components as the propane insoluble phase. This procedure was carried out as a continuous countercurrent process wherein the charge oil was fed in near the top of an extraction tower and propane in near the bottom. The propane to oil ratio was 10:1 by volume and extraction tower top and bottom temperatures were and 122 F., respectively. Internal tower pressure during the extraction was maintained at 450 p.s.i.g. The deasphalted oil product was taken oif the top of the tower in the form of an extract solution, sent through an oil fiash drum and through a stripper to remove all of the propane solvent. The yield of deasphalted oil was 55.8% by volume on charge and tested 22.6 API gravity, 565 F. flash point, 178 SUS at 210 F. viscosity, and had 3 Conradson carbon residue of 1.0.

This deasphalted oil was then subjected to a selective solvent extraction process to extract out undesirable sludge forming aromatic components. Aqueous phenol was the selective solvent used in this process. The extraction was carried out as a countercurrent process in a vertical extraction tower with the charge oil fed in near the bottom of the tower and the solvent in near the tower top. The phenol contained 1.8% water and an additional 0.3 water (on phenol) was fed in near the tower bottom. Extraction tower top and bottom temperatures were 205 and 213, respectively, and solvent to oil ratio was maintained at 2.69 by volume. The oil product was taken oii the top of the extraction tower in the form of a raffinate solution, put through a heater and stripper to steam strip out the solvent and yield 54.5% by volume of a waxy rafiinate' testing 28.0 API gravity, 575 F. flash, 134 SUS at 210 F. viscosity, and 120 F. pour point.

This waxy residual raifinate was then solvent dewaxed by diluting the charge oil with a 50/50 volume percent mixture of methylethyl ketone and toluene, chilling to a temperature of l F. and filtering out the waxy petrolatum component. The total solvent to oil ratio was 3.4:1 by volume. The pressed oil was then put through a heater flash tower and stripping tower to remove the dewaxing solvent and yield a dewaxed bright stock oil consisting of 71.9% on original waxy raffinate charge. This material tested as shown by the following table:

Physical properties of bright stock 1 1 hour at 350 F. in rotating oven.

Normal. finishing operations for such bright stocks consists of an earth adsorption process utilizing either clay contact or percolation techniques to efiect some improvement in color and oxidation stability properties of the oil. The method of finishing employed in accordance with our invention difiers from the normal finishing techniques in that in accordance with our invention a mild hydrogenation procedure is utilized. The improvement produced when our process is employed is shown by the information given below, in which a portion of the bright stock made as described was finished by hydrogenation in accordance with our invention and a portion was finished by earth contacting. The hydrofinishing andearth contacting were performed in accordance with the following processing conditions:

Process conditions for finishing step X Weight hourly space velocity (pounds of oil charge per pound of catalyst per hour).

3 Analyzed approximately 3% cobalt oxide and percent molybdic oxide by weight, the remainder being alumina.

A comparison of the products, after light steam stripping of the hydrofinished bright stock to remove dissolved hydrogen sulfide and residual light ends to yield 99.9 percent on charge, is as follows:

Hydro- Earth finished Finished Product Product Gravity, API 27.0 27.0 Flash, F 575 570 Fire, F 635 650 Viscosity, SUS at F. 2, 309 2, 650 Viscosity, SUS at 210 F. 141. 9 151. 6 Viscosity Index. 94. 5 92. 4 Pour, F 15 15 Color, NPA 4- 6- Color Stability (NPA).-. 4- to 5- 6- to 8- Oarbon Residue, Percent 0. 41 0. 50 Specific Dispersion" 116. 9 116. 5 Iodine No 12. 4 l4. 0 Aniline Point, 125. 7 125. 6 Sulfur, Percent..- 0.19 0. 22

The improved oxidation resistance of the hydrofinished oil is shown by the following test results:

A method for the manufacture of a bright stock of enhanced stability to oxidation consisting essentially of distilling a Mid-Continent crude to obtain an asphaltcontaining bottoms having an SSU viscosity at 210 F. of from 300 to 1200 seconds, deasphalting the bottoms to yield a deasphalted oil having a Conradson carbon residue of not greater than 2.25 percent, solvent extracting of the deasphalted oil to yield an oil which after dewaxing has a viscosity index of at least 85, dewaxing the solvent extracted oil to yield a bright stock having an ASTM pour point not above 20F. and a viscosity index of at least 85, and then hydrogenating the bright stock by passing it into contact with a cobalt molybdate supported on alumina catalyst at a temperature of from 500 to 725 F a pressure of from 300 to 700 p.s.i.g. and a weight hourly space velocity of from 3 to 15 while the bright stock is in admixture With from 500 to 2000 standard cubic feet of hydrogen per barrel of bright stock whereby from 10 to 30 standard cubic feet of hydrogen are reacted per barrel of bright stock.

References Cited in the file of this patent UNITED STATES PATENTS 

